Fan does not come on

I have a 96 Lumina 3.1 engine. My fan does not come on at all. I used to be able to get the driver side on by turning on the a/c, but that has stopped also. Temp gage works, fans work, relays work. When I disconnect the temp sensor both fans come on. I'm afraid that the computer is bad. I really don't want to spend $60/hr for somebody to tell me they don't know. Any ideas or steps I can do to confirm or discount the computer?

I think in the absence of a relevant coolant temp signal, it defaults to run both fans just in case...so the ECM is probably working OK.


Check the harness grounds to the engine, I think they are at one of the tranny bellhousing bolts up top. You didn't have tranny work done or something where wiring mighta got forgotten or something, did you?

I'll think about this some more and see if I can come up with a shadetree way to verify what's happening.

When you turn the A/C on, does the compressor run? If the system is low on charge, the compressor won't run. No compressor, no aux fan, they are linked together.

Oh, and BTW are you overheating? How high if so?

Oh, and BTW are you overheating? How high if so?
I do not have a graduated temp gage, but the temp gage does go about 3/4 of the way to red. Since it is cold out and I do commute downhill :) , I can control the temp to average a touch less than 50%.
No recent transmission work.
The a/c compressor does come on.

hmmm. Sounds like the fan circuit lost a ground to me...

Wait...no..because you said they come on when you unplug the cts. Damn.

Wait...no..because you said they come on when you unplug the cts. Damn.

Yeah. I was hoping this would be simple. I first thought it was a bad temp sensor, but the temp gage deflects normally. Both fan motors work. No recent work on the car. My last thought was the computer because of both fans not working. It is the only common thing, unless, like you say, there is a ground somewhere. Here's a question, how long can I go with both fans running?

Any more Ideas??

Yeah. I was hoping this would be simple. I first thought it was a bad temp sensor, but the temp gage deflects normally. Both fan motors work. No recent work on the car. My last thought was the computer because of both fans not working. It is the only common thing, unless, like you say, there is a ground somewhere. Here's a question, how long can I go with both fans running?

Forcing them to run will not really hurt anything, but will cause you problems in real cold weather, it may not put out much heat, will run too cold and waste fuel, etc. You might wanna unplug one if you are gonna drive it that way until you figure it out.

Did you consider you have two temp sensors, one for the ECM and one for the gauge? Maybe the other one is bad??

1. I was trying to figure that out, because (I guess) the temp sensor the Chilton's manual shows seems to only deal with the gage.
2. Where would it be located?
3. How could I test it?

Thanks!

I had the exact same problem on my 95. In fact, I ended up replacing the engine because of overheating. Its the temp sensor. Mine fans didn't work unless you unpluged it and my temp gauge worked fine. Cheap part. Should fix the prob.

I was in a parking lot for 45 mins yesterday trying to find a parking place so i could go inside and work... luckily i left early. my engine started getting right near the red, and i freak out when it gets anywhere near that... so i throw it in nuetral and give her about 2k rpms just so its quiet enough and brings it down. but i want to rig the fans on a switch so i can turn them on when i want.i have a 3 way switch, which i would make it work like this, Middle is off, Bottom is one fan, Top is both fans. i know electronics and im sure that is simple... can i just splice into that wire to make it work?

When I disconnect the temp sensor both fans come on.

That tells you it's the sensor and not the computer, or the fan wiring.